Note: I'm traveling during the holidays so updates will be infrequent.
The author claimed that many readers misinterpreted the red color as meaning high temperatures when he intended to show higher-than-normal temperatures. In other words, the readers did not recognize a relative scale is in play.
That is a minor issue that can be fixed by placing a label on the map.
There are several more irritants, starting with the abundance of what Ed Tufte calls chartjunk. The county boundaries do not serve a purpose, nor is it necessary to place so many place names. State boundaries too are too imposing. The legend fails to explain what the patch of green in Florida means.
The article itself links to a different view of this data on a newly launched site called Climate Prediction Center, by the National Oceanic and Atmospheric Administration (link). Here is a screenshot of the continental U.S.
This chart is the other extreme, bordering on too simple.
I'd suggest adding a little bit of interactivity to this chart, such as:
- Hiding the state boundaries and showing them on hover only
- Selectively print the names of major cities to help readers orient themselves
- Selectively print the names of larger cities around the color boundaries
- Using a different background map that focuses on the U.S. rather than the entire North American continent
This is a Type V chart.